Silver Niobate Research Articles

Investigations on the effect of preparation conditions on AgNbO 3 ceramics

AgNbO 3 ceramic was found to be one of the candidate materials for lead-free piezoelectric materials. The processing and sintering procedures have detrimental effect on the characteristics of the ceramics. Ceramic pellets of silver niobate, AgNbO 3 were prepared by solid-state reaction technique. To investigate the effect on the ceramic characteristics, two different sintering procedures were adopted. The crystallinity and surface morphology of the prepared samples were investigated by XRD and SEM techniques. The samples prepared by both the methods show orthorhombic structure at room temperature. Comparisons of lattice parameters, crystallite and grain sizes of AgNbO 3 are reported. Frequency variations of dielectric constant ( K), tangent loss (tan δ) and electrical conductivity ( σ) were measured at room temperature in the frequency range 1 Hz to 10 MHz.

Crystallographic phase stabilities and electronic structures in AgNbO3 by first-principles calculation

Silver niobate (AgNbO3) assumes several phases that crystallise in the perovskite structure similar to sodium niobate (NaNbO3). In order to investigate the phase stability of AgNbO3, the formation enthalpies of both physically the realised (real) cubic , tetragonal (P4/mbm) and orthorhombic (Cmcm, Pbcm) phases as well as the virtual phases, the orthorhombic (Pc21 b) and rhombohedral (R3cR) phases, which are observed in NaNbO3, have been obtained using a plane-wave pseudopotential method. Although the orthorhombic (Pbcm) phase has the lowest formation enthalpy among the real phases, the virtual rhombohedral (R3cR) phase has the lowest symmetry as well as the lowest formation enthalpy among all phases. We thus speculate that the rhombohedral (R3cR) phase may be stable at extremely low temperatures provided that it is accessible kinetically. In addition, the electronic structures of the various phases of AgNbO3 are calculated within the generalised gradient approximation with the Perdew–Burke–Ernzerhof correction (GGA-PBE). The valence band top was found to consist of predominately localised Ag 4d and O 2p orbitals constituting the O 2p–Nb 4d bonding orbital, while the bottom of the conduction band was found to mainly consist of the anti-bonding orbital of Nb 4d–O 2p under the Ag 5s orbital.

Lead-free piezoelectric ceramics derived from the K0.5Na0.5NbO3–AgNbO3 solid solution system

A lead-free solid solution between potassium sodium niobate and silver niobate, (1−x)K0.5Na0.5NbO3–xAgNbO3 (KNN-AN, with x=0–0.36), has been prepared in the form of ceramics by solid state reaction under O2 atmosphere. The crystal chemical study shows that Ag+ ion diffuses into the KNN lattices to form a solid solution of perovskite structure with x up to 0.30. The substitution of Ag+ ion for (K0.5Na0.5)+ ion results in linear decreases in the ferroelectric Curie temperature (TC), from 420°C in KNN down to 325°C in 0.70KNN-0.30AN, and in the tetragonal to orthorhombic phase transition temperature (TT-O), from 190 down to 150°C. The relative density of the KNN-AN ceramics reaches 94%. The optimum piezoelectric properties are found in the ceramics of 0.82KNN-0.18AN, with a piezocoefficient d33=186pC∕N, an electromechanical coupling factor kp=42.5%, and a TC=355°C. For the ceramics with x=0.24, the remanent polarization reaches a maximum value of Pr=20μC∕cm2, with a reduced coercive field Ec=6.4kV∕cm and a TC=340°C. It is shown that the (1−x)KNN-xAN ceramics exhibit piezoelectric properties which are comparable or superior to the hot-pressed KNN ceramics and other KNN-based systems. In particular, the piezoelectric properties exhibit very a good thermal stability up to high temperature, which is a significant improvement from other KNN-based piezoceramics.

AgTaO 3 and AgNbO 3 thin films by pulsed laser deposition

Silver tantalate AgTaO 3 (ATO) and silver niobate AgNbO 3 (ANO) films have been grown on to the LaAlO 3 (001) and sapphire Al 2O 3 (0112, r-cut) single crystals by pulsed laser deposition technique from stoichiometric ATO and ANO targets. X-ray diffraction study revealed epitaxial quality of ATO and ANO films on the LaAlO 3 (001) whereas on the sapphire r-cut substrate they are preferential (110) and (001) oriented. To characterize microwave films properties in the range from 1 to 40 GHz, coplanar line interdigital capacitors were fabricated by photolithography and lift-off technique. ANO film capacitors show superior properties: frequency dispersion was as low as 13%, voltage tunability (40 V, 200 kV/cm) was about 4.6% at 20 GHz, loss tangent ∼0.106 at 20 GHz, K-factor = tunability / tan δ from 49% @ 10 GHz to 33% at 40 GHz.

Growth of lithium doped silver niobate single crystals and their piezoelectric properties

Lithium doped silver niobate (Ag 1− x Li x NbO 3, 0 < x < 0.1) is one of the candidate materials for lead-free piezoelectric materials. In this study, Ag 1− x Li x NbO 3 single crystals were successfully grown by a slow cooling method. Crystal structure was assigned to perovskite-type orthorhombic (monoclinic) phase. Dielectric properties were measured as a function of temperature. As a result, with increasing lithium contents, the phase transition at around 60 °C was shifted to lower temperature while the phase transition at around 400 °C was shifted to higher temperature. On the basis of these peak shifts, the lithium contents in Ag 1− x Li x NbO 3 single crystals were determined. Moreover, P– E hysteresis measurement revealed that pure silver niobate crystal was weak ferroelectrics with P r of 0.095 μC/cm 2 while Ag 0.9Li 0.1NbO 3 (ALN10) crystal was normal ferroelectrics with P r of 10.68 μC/cm 2. About this ALN10 crystal, polling treatment was performed and finally piezoelectric properties were measured. As a result, high electromechanical coupling coefficient k 31 over 70% was observed.

Comparative Analysis of the Phonon Modes in AgNbO[sub 3] and NaNbO[sub 3

The lattice dynamics of silver niobate AgNbO3 and sodium niobate NaNbO3 is calculated from first principles. The unstable modes (i.e., tilting of oxygen octahedra and ferroelectric atomic displacements) in silver and sodium niobates are analyzed. It is shown that the existence of ferroelectric modes is associated primarily with the instability of the atomic positions of silver and sodium in the crystal lattice. The dynamic charges in the structure of silver and sodium niobates are determined. According to the first-principles calculations, both silver and sodium niobates in the ground state (T = 0) are characterized by ferroelectric atomic displacements and frozen tilting of oxygen octahedra, with the only difference being that the tilting modes of the oxygen octahedra in silver niobate correspond to the M point of the Brillouin zone, whereas those in sodium niobate are attributed to the R point of the Brillouin zone. The results of these calculations are in good agreement with experimental data.

Proposal of Li-doped Silver Niobate single crystals as lead-free piezoelectrics

Proposal of Li-doped Silver Niobate single crystals as lead-free piezoelectrics

Growth of Silver Niobate Based Single Crystals and Their Characterization

Growth of Silver Niobate Based Single Crystals and Their Characterization

Preparation and dielectric properties of Ag 1− xLi xNbO 3 (ALN) solid solutions ceramics

Ceramics of Ag 1− x Li x NbO 3 (ALN) solid solutions were sintered for Li concentration range 0≤ x≤0.1. They show a perovskite structure and exhibit the orthorhombic symmetry at room temperature. Low frequency (1 kHz–1 MHz) dielectric investigations were carried out for temperature range 120–920 K. The relaxor nature of weak ferroelectric M 1 phase in silver niobate AgNbO 3 was observed for first time. Three predominant aspects of Li substitution were found. The first one is associated with a large increase of spontaneous polarisation and with an emphasis on the relaxor character of the ferroelectric M 1 phase. The second one is related to a gradual increase of the broad ε( T) maximum associated with the transition between disordered antiferroelectric M 2 and M 3 phases. The third one is connected with a large increase of thermal hysteresis of the main M 3–O 1 phase transition, which points to the martensitic nature of this phase transition. The Li substitution influence is discussed in terms of the appearance of electric dipole moments linked with the occupation of the off-centre positions by Li ions.

Dielectric properties of Ag1-xAxNbO3 (A: K, Na and Li) andAgNb1-xTaxO3 solid solutions in the vicinity of diffuse phasetransitions

Low-frequency (100 Hz-1 MHz) dielectric studies of theAgNb1-xTaxO3 (ATN) (0⩽x⩽0.4), Ag1-xKxNbO3 (AKN)(0⩽x⩽0.04), Ag1-xLixNbO3 (ALN) (0⩽x⩽0.04) andAg1-xNaxNbO3 (ANN) (0⩽x⩽0.4) solid solution ceramics werecarried out in the temperature range 120-700 K. The dielectric dispersion wasonly observed within the ferroelectric M1 phase. For all the investigatedmaterials the M1-M2 phase transition exhibits the ferroelectricrelaxor-like character. The relations between the frequency and thetemperature (Tm) of the maximum dielectric permittivity ε' onlyobey the Vogel-Fulcher law for the ALN ceramics. Measurements of remanentpolarization Pr were performed within the ferroelectric M1 phase. Twodifferent origins of the ferroelectric state are proposed. The possibilitythat the M1 ferroelectric phase is of ferrielectric nature is alsodiscussed. The diffuse M2-M3 phase transition is frequency independent.These results allowed us to consider the coexistence of the ordered anddisordered subsystems in silver niobate and its solid solutions.

Reorientation of the W′ domain walls in ferroelastic silver niobate crystal

Using a polarizing microscope the temperature dependence of orientation of W′-type domain walls in a ferroelastic AgNbO3 crystal was determined. Results obtained are discussed within the framework of the Sapriel theory in relation to temperature dependence of lattice unit cell parameters. Inversion of the W′-domain wall orientation was observed.

An additional phase transition in silver niobate AgNbO3

Dielectric, DTA and domain structure investigations (300 K-750 K) have been carried out for ceramics and two types of single crystals of silver niobate AgNbO3. Additional phase of the orthorhombic symmetry has been found in temperature range 630 K-638 K.

Piezoelectric and ferroelectric properties of rare-earth modified filled tungsten bronze barium silver niobate ceramics

Abstract Ceramics of Ba4–2xAg2+xLnxNb10O30 where x = 0.0; 0.1; 0.3; and 0.5; Ln = Gd, Dy were prepared by conventional powder mixing method. XRD patterns of these materials indicated them to be orthorhombic. Substitution of rare-earth into barium silver niobate yielded a higher room temperature dielectric constant but lowered the Curie temperature from 415°C to 118°C with a significant decrease in the peak dielectric constant also. Rare-earth substituted samples showed higher electromechanical coupling coefficients. The micro-structure of these samples was studied by a scanning electron microscope.

Effect of rare earth substitution on the dielectric and piezoelectric properties of Ba2 Ag Nb5 O15

Abstract The present study deals with rare earth modified Barium Silver Niobate (BAN) of the composition Ba4–2× Ag2+× Ln=Nb10 O30 where Ln = Nd, Sm and 0 ≤ × ≤ 0.5. The effect of substitution of rare earth ions on the dielectric and piezoelectric properties of BAN are discussed in terms of micro-structure.

Electron microscopy of domain structures

Abstract In this survey the different imaging techniques used in the study by electron microscopy of domains and domain walls in solids are briefly summarized. In a first part the characteristic contrast features observed in electron micrographs of domains in a ‘single’ crystal are described for the different kinds of domain structures. An example of application to the problem of the configuration of domains and domain walls in silver niobate (AgNbO3) is discussed in a second part of this paper.

Thermal dilatation study of the phase transitions in silver niobate

Abstract The thermal expansion of silver niobate (AgNbO3) in combination with measurements of the dielectric properties are indicative of a sequence of phase transitions: two first order transitions at 360 and 590°C and a diffuse phase transition in the range of 150 – 350°C. Further evidence is given that the “dielectric” anomaly at 70°C reported in literature is due to an exponential relaxation process with an activation energy of 0.60 eV.

Raman scattering, central peak and phase transitions in AgNbO3

Light-scattering investigations in the temperature range from 10 to 850K have been performed on single crystals of silver niobate AgNbO3. The results are compared with structural and dielectric measurements revealing a complex sequence of phases. The Raman results and especially the strong central peak, which occurs over a wide range of frequencies and temperatures, are analysed in connection with the various phase transformations. The specific contributions of the niobium and the silver ions are tentatively discussed.

Central Peak and Soft Mode in AgNbO3

Silver niobate AgNbO3 is a perovskite compound which undergoes a complex series of structural phase transitions. Raman scattering experiments have been performed on single crystals between 300 and 650 K. The analysis of the data, in using a suitable lineshape Raman function, reveal the presence of a broad central component in addition to an underdamped soft phonon line. A very diffuse phase transition is found to be connected to the occurence of the central peak whereas a very sharp transition can be associated to the abrupt soft-phonon disappearance.

Ferrielectricity

A new group of materials has been found exhibiting ferroelectric behavior. It was found that this behavior appears in a mixture of antiferroelectric compounds (sodium vanadate and sodium niobate; also sodium niobate and silver niobate) neither of which exhibits this phenomenon at low field strength in their pure states. Coercivity as well as polarization is composition dependent. The onset of the ferroelectric state is a function of applied field, which in some compositions is considerably higher than the coercive field. Switching transients of a form not previously reported are exhibited by these materials.

Structural and electrical properties of silver niobate and silver tantalate

Structural and electrical properties of silver niobate and silver tantalate